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There are a huge number of pollutants resulting not just from rearing and feeding animals but from processing them, too. Livestock excreta contains a considerable amount of nitrogen , phosphorous, potassium, drug residues, heavy metals and pathogens (disease causing bacteria) and these pose serious threats to the environment. In 2004, it is estimated that 135 million tonnes of nitrogen and 58 million tons of phosphorous were produced from manure – cattle accounting for 58 per cent, pigs around 32 per cent and poultry seven per cent. To this has to be added the vast amounts of nitrogen used as chemical fertiliser on fodder crops (UN FAO, 2006).
Of these nutrients the most pressing concern is over nitrogen which, although a nutrient essential to all forms of life, is one you can have too much of. Nitrogen has to be ‘fixed’ – changed into a form available to plants by bacteria and blue-green algae (more recently renamed cyanobacteria) and under natural circumstances it is quite limited, a precious commodity.
All that has changed in the past few decades. Driven by a massive increase in the use of nitrogen fertiliser primarily for animal feed, the burning of fossil fuels and large scale clearing of forests, the amount of nitrogen available has doubled sine the 1940s. We now have the extraordinary situation where human-produced nitrogen is estimated at 210 million tonnes, greater than the world’s natural supply.
The threat of nitrogen overload was once concentrated in Western countries but is becoming a global threat with the spread of animal agriculture. Excess nitrogen can seriously damage the environment with just a few species of grass dominating and heathland, rich in species, giving way to conifer forests which host few species. It also poses a serious threat to human health and is linked to blue baby syndrome, a potentially fatal destruction of red blood cells in new-born children (Defra, 2003).
The gases nitrogen produces – nitric oxide and nitrous oxide – play a major role in causing smog, ozone depletion, global warming and acid rain – and they can claim 65 per cent of the blame for the latter.
Some of the greatest damage is done to waterways because of nitrogen run off. One half of all the commercial fertiliser ever produced has been applied since 1984. Only 50 per cent is taken up by vegetation, the other 50 per cent evaporating or being washed into groundwater or watercourses as run-off. It is joined by run-off from manure, both from grazing animals directly or when it used as manure. This poses one of the greatest threats to the aquatic environment.
Just as nitrogen fertilises the land so it fertilises water plant growth and algae, which can grow almost uncontrollably. When this vegetation dies and decays it can rob the water of oxygen, essentially suffocating fish and other aquatic organisms. It is a process known as eutrophication and isn’t confined to inland waterways but seriously damages estuaries and inshore waters too, where most fish and shellfish breed.
Partly enclosed seas such as the Baltic Sea, Black Sea and Mediterranean have been hit hard by eutrophication and a dead zone has developed in the Gulf of Mexico off the mouth of the Mississippi River (Roach, 2005). In fact, 150 of these dead zones have been identified – and there may well be more - some the size of small countries. The United Nations Environment Programme (UNEP) believes they will soon damage fishstocks even more than overfishing (UNEP, 2006).
Also increasing are the number of toxic algal blooms covering vast areas of seas and inland waterways and are a threat to human and other lives.
It beggars belief that the world is still anticipating rapid growth in livestock and fodder production when even the present levels are wreaking havoc on a scale that is entirely new to the planet and entirely unsustainable.
Manure poses other threats and is present in great quantity. It is estimated that the US cattle herd alone produces 253,924 pounds of manure a second (Gellatley J, 1996). Worldwide, livestock produce in excess of 13 billion tonnes of excreta a year (CIWF, 2004). Apart from its threat to the environment, more than 40 diseases can be caught by humans from manure (NRDC 2005).
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